Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$132.89	10.435%	$146.7571	$146.76	$146.75	$146.80
Purchase #2	$153.46	8.508%	$166.5164	$166.52	$166.50	$166.50
Purchase #3	$203.40	9.442%	$222.605	$222.61	$222.60	$222.60
Purchase #4	$39.48	11.503%	$44.0214	$44.02	$44.00	$44.00
Purchase #5	$16.42	12.747%	$18.5131	$18.51	$18.50	$18.50
Purchase #6	$196.68	8.176%	$212.7606	$212.76	$212.75	$212.80
Purchase #7	$99.35	6.539%	$105.8465	$105.85	$105.85	$105.80
7 purchase totals =	$841.68		$917.0201	$917.03	$916.95	$917.00